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Just build this nice amp to a protoboard for testing but for some reason the other mosfet and R4 are warming quite a lot and the original 0.6W R4 was smoking. So I swapped 8.2ohm 5W in place for R4 and measured 520 mA through it. The other channel's R4 draws only 137 mA which i think is normal. Any tips for troubleshooting? I haven't noticed any mistakes in wiring and it's pretty much identical to the other channel.

The amp otherwise is working and I can hear both channels and they seem to in balance.

Built this little amp a week ago and i just can´t get it to work... every voltage seems to be fine, the voltages on the pins, on the mosfet and the lm317. But no sound. I tried diffrent potentiometers, inputs, headphone jacks and no diffrence. Can the MOSFET´s be damaged if they put out the right voltages?

Hi all, i am planning to start this weekend. Have soent about 30 pounds at conrad on parts and excited to build this with my son. Open question for me is how to check the 'dc offset'? I take it i turn on the amp, have no music playing and check potential difference between channel out and earth? What happens if it great than 10mv? An indication that something isnt right?I am thinking of buying multiple resistors of the same values then measuring them with DMM and using as best matched pairs i can on each channel?Thanks all, Richard

Shoo wow, 163 pages and a lot of time later I have finished reading the thread.

This is not my first amp build, built some small CMOYs and a O2 from JDS Labs.

This is my first Tube Amp build and I love it.I was lucky enough to find a local guy who had had some really neat compact PCBs etched. The amp runs great although very hot so heat sinks are on the plans for the weekend. Was also lucky with power supply, the second one I pulled out my box of bits worked perfectly and is dead silent.

I have a Little Bear P1 Tube Amp and I think this new one sounds better. (I suppose there is the I built this myself factor that affects the sound).

I want to protect my headphones from the thump and know I need to put a delay circuit on the amp. I am looking at viewtopic.php?f=10&t=1480 for the details.

My question is, where in the amp circuit do I put this?I assume it is between power and amp, but not sure at all.(or does it make up part of a regulated supply)

Yippie, built this over about 8 hours this weekend. Running off a wallwart, little hum, have 50k alps pot on input with gets noisy the higher the volume. Amp sounds bass heavy on cheap headphones and bass light on grado 325's. Currently using no name valve, cheapest conrad.ch had. Buying two GE JAN,s tonight, see how they fair. May try 1uF input cap see if bass improves? Want to build one as a pre amp? Any suggested changes when running as a pre amp?Fantastic project. May build for friends and family and give as crimbo presents

Yippie, built this over about 8 hours this weekend. Running off a wallwart, little hum, have 50k alps pot on input with gets noisy the higher the volume. Amp sounds bass heavy on cheap headphones and bass light on grado 325's. Currently using no name valve, cheapest conrad.ch had. Buying two GE JAN,s tonight, see how they fair. May try 1uF input cap see if bass improves? Want to build one as a pre amp? Any suggested changes when running as a pre amp?Fantastic project. May build for friends and family and give as crimbo presents

Is your supply regulated or a switch mode? Normally non regualted supplies and these type of low ripple rejction circuits have allot of hum.

You are using a 0.1uF right now? what size is your output cap? is it 4700uF. If your already these values changing your 0.1uF would not increase bass however you can try. (0.22uF would be good as it will not distort your square as much while providing one times lower cutt of freq) (EDIT: I thought I was making a reply for MCA - Son of ZCA)

As a pre amp, your output cap would only need to be 2.2uF or higher, 1.5uF has a cut off of about 10hz with a 10k load. You can chose high quality metalised polypropene for better sound.

Last edited by KochiyaYamato on 05 Nov 2017, 19:16, edited 2 times in total.

Hi KochiyaYamato,Thanks for the reply. Currently running the amp stock, so 2.2uf on input and 470uF output.Not sure about the wallwart, some little Phillips affair. Better that the laptop 12v I tried which was crazy noisy. Source tried so far is an iPod shuffle.... So what should I expect!!! Will hook up to my cd850mk2 after 12hours burn in. I've seen an additional cap to Earth on the input side could help with noise, and a 1000uF on the power supply could help. Will pick up a 12v pub battery tomorrow and see if that helps. Will definitely build more and try tinker a little to match better to my headphones. The thump worries me but can workaround with the right plugin order. Can't find a good schematic for the 12v thump delay. Missed out on the ge Jan valves sure something else will come up. Am sure I will go higher voltage at some point but need to know what I am talking about first!!! I've also got the oatley low voltage headphone amp, has much more fun with this one so far

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